Any ideas how to get 11yr old to mind her own business?

DD2 is always looking to see my login/password/PIN, same when DD1 uses her phone, told friends the password for DD1's laptop and today told a visiting friend (of DD1's) that another friend can't visit because she is being punished for doing X, her punishment is X and it's to last X amount of time.

She can't see why these things would wind anyone up, and she's just like grandma who I avoid speaking to because she's a blabber mouth

I really am at a loss as to how to get her to see that what she's doing is wrong and will wind people up, and they will start to avoid her. Explaining isn't helping, neither telling her off or withdrawing priveledges. I have thought of an old fashioned gag, but the PC police probably wouldn't like it.

Might try that again Feilefoo, thanks. She gets all narky and viscous of course if anyone says anything about her so we had stopped because she was taking it out on DD1. I reckon she's old enough to be expected to grasp the concept now.